1. Field of the Invention
The present invention relates to a sheet conveying device for conveying sheet, and an image forming apparatus including this sheet conveying device.
2. Description of the Related Art
An image forming apparatus spreading in recent years fixes a toner image to sheet, conveys the sheet to a curved conveyance path, and discharges the sheet by using a pair of discharge rollers disposed on the downstream side of the conveyance path. This type of image forming apparatus conveys the sheet in the vertical direction after transfer of the toner image to the sheet to fix the toner image, and then conveys the sheet in the horizontal direction to discharge the sheet, for example.
According to the image forming apparatus having this structure, the sheet conveyed to the curved conveyance path contacts an outer circumferential wall of a curved portion of the conveyance path, and travels toward the pair of discharge rollers while guided by the curved conveyance path. A sheet conveying device disclosed in JP 2008-120543 A is configured to withdraw a guiding portion provided for guiding a rear end of sheet so as to reduce noise generated by collision between the guiding portion and the rear end of the sheet.
According to the foregoing image forming apparatus, the sheet easily contacts the outer circumferential wall while passing through the curved conveyance path. Particularly at the time of double-sided printing, the temperature of the toner image fixed to a first surface of the sheet is raised high by heat generated from a fixing unit. In this case, the toner image may fuse and produce an abnormal image as a result of contact between the fused toner image and the outer circumferential wall. This problem becomes more conspicuous when the circumferential speed of the pair of discharge rollers is lower than the circumferential speed of a pair of fixing rollers, for example, in which condition the sheet easily bends in a loop shape.
In case of a structure which forms sheet feed ribs on the outer circumferential wall, these ribs may produce not only an abnormal image containing stripe marks in correspondence with the ribs, but also accumulation and congealment of fused toner on the ribs. When this accumulation occurs, the deposit of toner may scratch the image printed on the outer surface of the sheet. These scratches may produce an abnormal image containing white stripes as a result of exposure of the base of the sheet, or cause damage to the sheet. In recent years, the use of toner fusible at a low temperature is increasing in view of power consumption reduction or for other reasons. Accordingly, this damage is becoming more conspicuous than ever.
It is preferable that the sheet to be conveyed does not contact parts of the apparatus more than necessary in view of quality maintenance of the sheet, for example, in either case of single-sided printing or double-sided printing. Accordingly, such consideration is preferably given which minimizes the contact between the sheet and the outer circumferential wall while the sheet is passing through the curved conveyance path.